Alpha-synuclein (alphaSN) brain pathology is a conspicuous feature of several neurodegenerative diseases, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), the Lewy body variant of Alzheimer's disease (LBVAD), multiple systems atrophy (MSA), and neurodegeneration with brain iron accumulation type-1 (NBIA-1). Common to all of these diseases, termed synucleinopathies, are proteinaceous insoluble inclusions in the neurons and the glia which are composed primarily of alphaSN.
Lewy bodies and Lewy neurites are intraneuronal inclusions which primarily contain of alphaSN. Lewy bodies and Lewy neurites are the neuropathological hallmarks Parkinson's disease (PD). PD and other synucleinopathic diseases have been collectively referred to as Lewy body disease (LBD). LBD is characterized by degeneration of the dopaminergic system, motor alterations, cognitive impairment, and formation of Lewy bodies (LBs). (McKeith et al., Clinical and pathological diagnosis of dementia with Lewy bodies (DLB): Report of the CDLB International. Workshop, Neurology (1996) 47:1113-24). Other LBDs include diffuse Lewy body disease (DLBD), Lewy body variant of Alzheimer's disease (LBVAD), combined PD and Alzheimer's disease (AD), and multiple systems atrophy. Dementia with Lewy bodies (DLB) is a term coined to reconcile differences in the terminology of LBDs.
Disorders with LBs continue to be a common cause for movement disorders and cognitive deterioration in the aging population (Galasko et al., Arch. Neurol. (1994) 51:888-95). Although their incidence continues to increase creating a serious public health problem, to date these disorders are neither curable nor preventable and understanding the causes and pathogenesis of PD is critical towards developing new treatments (Tanner et al., Curr. Opin. Neurol. (2000) 13:427-30). The cause for PD is controversial and multiple factors have been proposed to play a role, including various neurotoxins and genetic susceptibility factors.
In recent years, new hope for understanding the pathogenesis of PD has emerged. Specifically, several studies have shown that the synaptic protein alpha-SN plays a central role in PD pathogenesis since: (1) this protein accumulates in LBs (Spillantini et al., Nature (1997) 388:839-40; Takeda et al., AM J. Pathol. (1998) 152:367-72; Wakabayashi et al., Neurosci. Lett. (1997) 239:45-8), (2) mutations in the alpha-SN gene co-segregate with rare familial forms of parkinsonism (Kruger et al., Nature Gen. (1998) 18:106-8; Polymeropoulos M H, et al., Science (1997) 276:2045-7) and, (3) its overexpression in transgenic mice (Masliah et al., Science (2000) 287:1265-9) and Drosophila (Feany et al., Nature (2000) 404:394-8) mimics several pathological aspects of PD. Thus, the fact that accumulation of alpha-SN in the brain is associated with similar morphological and neurological alterations in species as diverse as humans, mice, and flies suggests that this molecule contributes to the development of PD.
Alpha-SN is part of a large family of proteins including beta- and gamma-synuclein and synoretin. Alpha-SN is expressed in the normal state associated with synapses and is believed to play a role in neural plasticity, learning and memory. Mutations in human (h) alpha-SN that enhance the aggregation of alpha-SN have been identified (Ala30Pro and Ala53Thr) and are associated with rare forms of autosomal dominant forms of PD. The mechanism by which these mutations increase the propensity of alpha-SN to aggregate are unknown.